O18 scrambling studies of kinases, pyruvate carboxylase, and photophosphorylation will continue. The mechanism of biotin enzymes will be studied by determining if under conditions where carboxybiotin is decarboxylated the product is CO2 or bicarbonate. The rate of dissociation of the substrate proton from aconitase will be determined by isotope trapping. BIBLIOGRAPHIC REFERENCES: Rose, I.A. and Hanson, K.R. Interpretations of the stereochemistry of enzyme-catalyzed reactions. Application of Biomedical Systems in Chemistry, Part II, (J. Bryan Jones, ed.), John Wiley and Sons, Inc., p. 507, 1976. Midelfort, C.F., Rose, I.A. and Gupta, R.K. Fructose-1,6-bisphosphate: Isomeric composition, kinetics, and substrate specificity for the aldolases. Biochemistry 15:2178, 1976.